Semiconductor device and fabrication method thereof

ABSTRACT

A semiconductor device and fabrication method thereof restrains an amplified current between input voltage Vin and ground voltage Vss, and first and second n-wells are biased into internal voltage sources, whereby the current-voltage characteristic of the input pad becomes stabilized during an open/short checkup of a semiconductor device. The semiconductor device includes a semiconductor substrate having a plurality of device isolation regions, first and second n-wells horizontally spaced from either of the plurality of device isolation regions, a p-channel transistor formed in the second n-well, an input protection transistor horizontally spaced from the first n-well and the device isolation region, on a symmetrical portion by the first n-well to the second n-well, and a guard ring formed between the first n-well and the input protection transistor.

This is a Continuation application of prior application Ser. No.10/868,216 filed Jun. 16, 2004, which is a Divisional of priorapplication Ser. No. 10/252,410 filed Sep. 24, 2002, which is adivisional of application Ser. No. 09/671,264 filed on Sep. 28, 2000,now U.S. Pat. No. 6,475,861, which is a divisional of application Ser.No. 09/056,618 filed Apr. 8, 1998, now U.S. Pat. No. 6,150,701, andwhich claims priority to Korean Patent Application No. 66665/1997 filedon Dec. 8, 1997, the disclosures thereof being incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor, and more particularlyto an improved semiconductor device and fabrication method thereof forforming a guard ring between n-wells provided for fabricating aperipheral circuitry adjacent to an input protection transistor, therebystabilizing a current-voltage operation characteristic of an input pad.

2. Description of the Background Art

Among semiconductor devices, a DRAM (Dynamic Random Access Memory)refers to a memory device wherein a basic cell is provided with aselection transistor and a capacitor. A gate of the selection transistoris connected to a word line, a drain thereof is connected to a bit line,and a source thereof is connected to an electrode or the capacitor, thatis, to an earthed electrode. Such a DRAM stores therein data dependingupon whether there is an electrical charge loaded in the capacitor. TheDRAM developed in the 1970's is still being studied for its largerintegration.

FIG. 1 is a cross-sectional view illustrating a semiconductor devicewith regard to an input pad peripheral circuit according to a backgroundart. As shown therein, a plurality of device isolation regions a, b, care formed in the upper surface of a semiconductor substrate 10. A firstand second n-wells 20, 30 are formed adjacent to the device isolationregions a, b in the semiconductor substrate 10. The first and secondn-wells 20, 30 are isolated by the device isolation region b. In thefirst n-well 20 there is formed an n+ diffusion layer 21 which isconnected to a first supply voltage Vdd. In the second n-well 30 thereare formed an p+ diffusion layer 31 which is connected to first supplyvoltage Vdd, and a p+ diffusion layer 32 which is connected to a secondsupply voltage Vcc. A p-channel transistor Q2 having the p+ diffusionlayers 31, 32 as drain and source and having a gate electrode G2 isformed in the second n-well 30. The first supply voltage Vdd denotes aninternal supply voltage generated from an externally applied supplyvoltage Vcc and is generally lower than the externally applied supplyvoltage Vcc. To the left side from the first n-well 20, there isprovided an input protection transistor Q1 adjacent to the deviceisolation region a. The input protection transistor Q1 is an n-channeltransistor. The n-channel transistor Q1 includes the gate electrode G1formed in the upper surface of the semiconductor substrate 10, and then+ diffusion layers 11, 12 as source and drain, respectively. The gateelectrode of the input protection transistor Q1 and the n+ diffusionlayer 12 are connected to a ground voltage Vss serving as a third supplyvoltage. The n+ diffusion layer 11 is connected to an input voltage Vinwhich is received from an input pad (not shown). An n+ diffusion layer13 is horizontally spaced from the left side of the input protectiontransistor Q1 and adjacent to the device isolation region c, and it isconnected to the third supply voltage. A horizontal npn parasite bipolartransistor Q3 is formed by the n+ diffusion layer 11 connected to theinput voltage Vin of the input protection transistor Q1 and by the n+diffusion layer 13 connected to the third supply voltage Vss.

Voltage V_(GD) connected to the gate electrode G2 of the p-channeltransistor Q2 denotes a voltage applied to the gate of the p-channeltransistor Q2 and a voltage of 0V is applied thereto. Here, voltageV_(BB) denotes a back bias voltage.

In the input pad peripheral circuitry as shown in FIG. 1, when the inputvoltage Vin is less than a threshold voltage Vth, the input protectiontransistor Q1 is turned on, thereby allowing current to flow to an inputvoltage Vin of the input protection transistor Q1.

Here, when a temperature goes up, electron-hole pairs are generated froma deletion region provided between the first n-well 20 and the p-typesemiconductor substrate 10, whereby holes h+ flow toward the p-typesemiconductor substrate 10, and electrons e− flow toward the firstn-well 20.

At this time, the first n-well is in a floating state so that thereceived electrons e− serve to lower the voltage, whereby a forwardvoltage is applied between the first n-well 20 and the p-typesemiconductor substrate 10. Accordingly, electrons are injected towardthe p-type semiconductor substrate 10.

When electrons are injected into the p-type semiconductor substrate 10,the injected electrons are turned to a base current of parasite bipolartransistor Q3, and the current amplified as much as the gate of thetransistor is applied between n+ region 11 to which is applied Vin andn+ region 13 which is connected to Vss.

As a result, when the first n-well 20 and the second n-well 30 arebiased by Vdd and an open/short test is carried out, a stablecurrent-voltage characteristic is not realized around the input padperipheral circuitry.

That is, the input pad peripheral circuitry of the conventional DRAMdevice according to the conventional art has several disadvantages:firstly, because the input protection transistor Q1 is activated by athermal carrier generated in a high temperature, there is a strongpossibility of incurring an operational error in the DRAM device; andsecondly, when carrying out an open/short test by biasing the n-wellregions 20, 30 to the first supply voltage Vdd, the n-well regionsrespectively remain in a floating state, thereby incurring a deviceerror in a high possibility.

SUMMARY OF THE INVENTION

The present invention is devised to solve the above-described problem.Accordingly, it is an object of the present invention to provide asemiconductor device and fabrication method thereof which makes itpossible to realize a stabilized current-voltage characteristic duringan open/short test in an input pad peripheral circuitry by forming aguard ring between an input protection transistor and a first n-welladjacent to the transistor.

To achieve the above-described object, there is provided a semiconductordevice according to the present invention which includes a semiconductorsubstrate having a plurality of device isolation regions, first andsecond n-wells horizontally spaced from either of the plurality ofdevice isolation regions, a p-channel transistor formed in the secondn-well, an input protection transistor horizontally spaced from thefirst n-well and the device isolation region, on a symmetrical portionby the first n-well to the second n-well, and a guard ring formedbetween the first n-well and the input protection transistor.

Further, to achieve the above-described object, there is provided asemiconductor device fabrication method according to the presentinvention which includes the steps of preparing a semiconductorsubstrate having a device isolation region, forming a first mask patternon a surface portion of the semiconductor substrate which is not toinclude first and second n-wells, implanting n-type impurities into thesemiconductor substrate to form the first and second n-wells, removingthe first mask pattern, forming a first gate electrode over a surfaceportion of the semiconductor substrate which does not include any ofn-wells, and a second gate electrode over the second n-well, forming asecond mask pattern on the second n-well and the second gate electrode,implanting n+ impurities into each side portion from the grist gateelectrode and the first n-well which are not covered with the secondmask pattern to form an n+ diffusion layer, removing the second maskpattern, forming a p+ diffusion layer on each side portion from thesecond gate electrode in the second n-well, and forming a guard ringalong an interface between the semiconductor substrate and the firstn-well.

Still further, to achieve the above-described object, there is provideda semiconductor device fabrication method according to the presentinvention which includes the steps of preparing a semiconductorsubstrate having a device isolation region, forming a third mask patternon a surface portion of the semiconductor substrate which is not toinclude first, second and third n-wells, implanting n-type impuritiesinto the semiconductor substrate to form the first, second and thirdn-wells, removing the third mask pattern, forming a first gate electrodeover a surface portion of the semiconductor substrate which does notinclude any of n-wells, and a second gate electrode over the secondn-well, forming a fourth mask pattern on the second n-well and thesecond gate electrode, implanting n+ impurities into each side portionfrom the grist gate electrode and the first n-well which are not coveredwith the fourth mask pattern to form an n+ diffusion layer, removing thefourth mask pattern, and forming a p+ diffusion layer on each sideportion from the second gate electrode in the second n-well.

The object and advantages of the present invention will become morereadily apparent from the detailed description given hereinafter.However, it should be understood that the detailed description andspecific example, while indicating a preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art from this detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become better understood with reference tothe accompanying drawings which are given only by way of illustrationand thus are not limitative of the present invention, wherein:

FIG. 1 is a schematic cross-sectional view illustrating a semiconductordevice with regard to an input pad peripheral circuitry according to abackground art;

FIG. 2 is a schematic cross-sectional view illustrating a semiconductordevice of an input pad peripheral circuitry according to a firstembodiment of the present invention;

FIG. 3 is a schematic cross-sectional view illustrating a semiconductordevice of an input pad peripheral circuitry according to a secondembodiment of the present invention; and

FIG. 4 is a schematic cross-sectional view illustrating a semiconductordevice of an input pad peripheral circuitry according to a thirdembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to the accompanying drawings, the semiconductor deviceand fabrication method thereof will now be described.

FIG. 2 is a cross-sectional view illustrating a semiconductor devicewith regard to an input pad peripheral circuitry according to the firstembodiment of the present invention. As shown therein, the input padperipheral structure of a DRAM device according to the first embodimentof the present invention is basically identical to that of thebackground art with the exception of a first n-well 20 and a guard ring40 serving as an oxide film formed along a side interface of thesemiconductor substrate 10.

That is, the peripheral circuit of a semiconductor device includes aplurality of device isolation regions a, b, c in the surface of thep-type semiconductor substrate 10. The first n-well 20 and the secondn-well 30 are formed in a right side portion of the semiconductorsubstrate 10 to have the device isolation region a formed therebetween.The first n-well 20 and the second n-well 30 are spaced by the deviceisolation region b. An n+ diffusion layer 21 connected to the firstsource voltage Vdd is formed in the first n-well 20. Also, the p+diffusion layer 31 connected to Vdd and the p+ diffusion layer 32connected to the second source voltage Vcc are formed in the secondn-well 30. A p-channel transistor Q2 has p+ diffusion layers 31, 32 assource and drain, and includes a gate electrode G2 in the second n-well30. The Vdd denotes an internal source voltage generated from anexternally generated source voltage Vcc and it has a lower voltage thana common Vcc. An oxide Film 40 serving as a guard ring is formed on atleast one side boundary between the first n-well 20 and thesemiconductor substrate 10. Also, an input protection transistor Q1 ishorizontally spaced from the device isolation region a in the left sideof the first n-well 20. Here, the input protection transistor Q1 is ann-channel transistor. The n-channel transistor Q1 includes a gateelectrode G1 formed in an upper portion of the semiconductor substrate10, and n+ diffusion layers 11, 12 formed in each side of the gateelectrode G1 respectively serves as source and drain of the n-channeltransistor Q1. The gate electrode G1 of the input protection transistorQ1 and the n+ diffusion layer 12 are connected to ground voltage Vssserving as a third source voltage, and the n+ diffusion layer 11 isconnected to an input voltage Vin outputted from the input pad (notshown). The n+ diffusion layer 13 connected to the third source voltageis formed to the left side of the device isolation region C which isspaced from the input protection transistor Q1. A horizontal npnparasite bipolar transistor Q3 is formed by the n+ diffusion layer 11connected to the input voltage Vin of the input protection transistor Q1and the third source voltage Vss.

Ground voltage V_(GD) connected to a gate electrode G2 of the p-channeltransistor Q2 denotes a voltage which is to be applied to the gate ofthe p-channel transistor Q2, and 0V is applied thereto. Voltage V_(BB)denotes a back bias voltage.

The semiconductor device fabrication method according to the firstembodiment of the present invention will now be described.

First, a plurality of device isolation regions a, b, c are formed in thep-type semiconductor substrate 10. Then, a first mask pattern is formedon the upper surface of the semiconductor substrate other than theregions for forming first and second n-wells 20, 30, and n typeimpurities are implanted into the semiconductor substrate for therebyforming the first and second n-wells 20, 30.

Then, the first mask pattern is removed.

The first and second gate electrodes G1, G2 are formed over a left sideportion of the device isolation region a of the semiconductor substrate10 and over the second n-well 30.

A second mask pattern is formed on the upper surface of the secondn-well 30, and n+impurities are implanted into each side portion of thefirst gate electrode G1 and the first n-well 20 to form n+ diffusionlayers 11, 12, 13, 21.

Then, the second mask pattern is removed.

A third mask pattern is formed to cover an entire structure of thesemiconductor substrate other than the second n-well 30, and p-typeimpurities are ion-implanted into the well 30 on each side of the secondgate electrode G2 which is provided over the second n-well 30.

As a result, the parasite bipolar transistor Q3 and the input protectiontransistor Q1 serving as the n-channel transistor are formed to the leftside of the first n-well 20, and the p-channel transistor Q2 is formedto the right side of the first n-well 20 and in the second n-well 30.

Oxygen ions are implanted into an interface of the first n-well 20 andthe semiconductor substrate 10 by use of an ion-implanting technique,and annealed to form an oxygen film serving as a guard ring 40 along theinterface, thereby completing the fabrication steps according to thefirst embodiment of the present invention.

The specific operational characteristics of the semiconductor devicefabricated according to the above-described steps will now be explained.

When Vin is less than threshold voltage Vth of the input protectiontransistor Q1, the input protection transistor Q1 is turned on, so thatthere flows a current in the source voltage Vin of the input protectiontransistor Q1. When the temperature is raised in the above state, thereare formed pairs of electrons e⁻ and holes h⁺, so that the holes h⁺ flowtowards the p-type semiconductor substrate 10 and the electrons e⁻ flowtowards the first n-well 20.

At this time, the first n-well 20 is in a floating state, so that thegenerated electrons cause the voltage of the first n-well 20 to becomelower, and accordingly when a forward direction voltage is appliedbetween the first n-well 20 and the p-type semiconductor substrate 10,the electrons are injected toward to the p-type semiconductor substrate10. Here, when the electrons are injected into the p-type semiconductorsubstrate 10, the guard ring 40 serves to prevent the electrons frombeing moved toward the base of the parasite bipolar transistor Q3.

Consequently, when the guard ring 40 is not formed, the injectedelectrons are turned to a base current of the parasite bipolartransistor Q3, so that an amplification current is prevented fromoccurring between the source input terminal Vin and the ground voltageVss.

The structure of the input pad peripheral circuitry of a semiconductordevice according to the second embodiment of the present invention willnow be described.

Instead of the guard ring 40, a trench 50 is formed along an interfacebetween the first n-well 20 and the semiconductor substrate 10, and anoxide film 50 is formed inside the trench 50. The other fabricationsteps for the second embodiment is identical to those of the firstembodiment of the present invention.

The fabrication steps of the semiconductor device according to thesecond embodiment of the present invention will now be described.

In accordance with the fabrication steps adopted in the first embodimentof the present invention, there are formed an input protectiontransistor Q1, a first n-well 20, a second n-well 30, and a p-channeltransistor Q2 in the semiconductor substrate 10.

Instead of injecting oxygen ions along an interface between the firstn-well 20 and the semiconductor substrate, a trench 50 is formedadjacent to the interface. Here, an anisotropic technique is employed toform the trench 50.

Then, the trench 50 is filled with an oxide film 51 by use of ahigh-temperature low-pressure deposition (HLD) method.

FIG. 4 is a cross-sectional view illustrating an input pad peripheralcircuitry of a semiconductor device according to the third embodiment ofthe present invention. As shown therein, the input pad peripheralcircuit structure according to the third embodiment of the presentinvention includes a third n-well 60 formed between a first n-well 20and the input protection transistor Q1, and an n+ diffusion layer 61formed on the surface of the third n-well 60 is connected to secondsource voltage Vcc, wherein the structure other than those elements isidentical to that of the conventional art.

The operation principles of the third embodiment of the presentinvention are as follows.

Under a high temperature, pairs of electron-hole are generated betweenthe first n-well 20 and the semiconductor substrate 10. The holes traveltowards the p-type semiconductor substrate 10, and the electrons movetowards the first n-well 20, so that there is formed a forward directionbias between the semiconductor substrate 10 and the first n-well 20, andaccordingly the electrons move again towards the p-type semiconductorsubstrate 10. At this time, the third n-well 60 is connected to thesecond source voltage Vcc, which is higher than the first source voltageVdd. Therefore, the electrons injected from the first n-well 20 towardsthe p-type semiconductor substrate 10 are guided towards the thirdn-well 60 having a high voltage to become a base current of theparasitic bipolar transistor Q3 of the p-type semiconductor substrate10, thereby restraining the amplification of a current which flowsbetween the input source terminal Vin and the n+ diffusion layer 13which receives the voltage Vss and accordingly stabilizing a sourcevoltage characteristic of the input pad periphery.

The fabrication method of the semiconductor device according to thethird embodiment of the present invention will now be described.

First, a plurality of device isolation regions a, b, c, d, e are formedin the upper surface of the p-type semiconductor substrate 10.

A third mask pattern (not shown) is formed on the upper surface of thesemiconductor substrate 10 other than regions in which first, second andthird n-wells 20, 30, 60 are to be formed.

Then, n-type impurities are implanted into the surface portion of thesemiconductor substrate 10 which is not covered by the mask pattern (notshown) to form the first, second and third n-wells 20, 30, 60.

Next, the third mask pattern (not shown) is removed.

A first and second gate electrodes G1, G2 are formed over the surfaceportion of the semiconductor substrate 10 which does not includes any ofn-wells and over the second n-well 30.

Then, the second n-well 30 is covered by a fourth mask pattern (notshown).

Thereafter, n+ impurities are implanted into each side portion of thefirst gate electrode G1 and into the first and third wells 20, 60 toform n+ diffusion regions 11, 12, 13, 21, 61, and then the fourth maskpattern (not shown) is removed.

A new mask pattern (not shown) is formed on the surface of thesemiconductor substrate 10 with the exception of the upper surface ofthe second n-well 30, and p+ impurities are implanted into each sidefrom the second gate electrode G2 on the second n-well 30 to form p+diffusion regions 31, 32.

As a result, the third n-well 60 is formed between the first n-well 20and the n-channel input protection transistor Q1 so as to serve as aguard ring.

As described above, the guard ring is formed between the inputprotection transistor Q1 and its peripheral n-well to restrain anamplified current between the input voltage Vin and the ground voltageVss, and the first and second n-wells of the input pad peripheralcircuit are biased into internal voltage sources, whereby thecurrent-voltage characteristic of the input pad becomes stabilizedduring an open/short checkup of a DRAM device.

As the present invention may be embodied in several forms withoutdeparting from the spirit of essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims, and therefore allchanges and modifications that fall within meets and bounds of theclaims, or equivalences of such meets and bounds are therefore intendedto embrace the appended claims.

1. A semiconductor device, comprising: a substrate; a first impuritywell formed in the substrate; a second impurity well formed in thesubstrate; and first, second, third and fourth diffusion layershorizontally disposed across the substrate, wherein the third diffusionlayer is disposed over the first impurity well and the fourth diffusionlayer is disposed over the second impurity well, and wherein the thirddiffusion layer and the first impurity well are configured to suppress acurrent flow between the first diffusion layer and the second impuritywell.
 2. The semiconductor device of claim 1, wherein the firstdiffusion layer and the third diffusion layer are configured tocommunicate with a first and a second voltage source, respectively. 3.The semiconductor device of claim 1, wherein the first diffusion layeris a component of a first portion of the semiconductor device.
 4. Thesemiconductor device of claim 3, wherein the first portion of thesemiconductor device comprises a diode.
 5. The semiconductor device ofclaim 3, wherein the first portion of the semiconductor device comprisesan input protection transistor.
 6. The semiconductor device of claim 5,wherein the first diffusion layer comprises a source of the inputprotection transistor and the second diffusion layer comprises a drainof the input protection transistor.
 7. The semiconductor device of claim1, further comprising a third impurity well formed in the semiconductorsubstrate and disposed proximate the second impurity well.
 8. Thesemiconductor device of claim 7, wherein the third impurity well is acomponent of a second portion of the semiconductor device.
 9. Thesemiconductor device of claim 8, wherein the second portion of thesemiconductor device comprises a diode.
 10. The semiconductor device ofclaim 8, wherein the second portion of the semiconductor devicecomprises a p-channel transistor.
 11. The semiconductor device of claim1, wherein the third diffusion layer and the first impurity well areconfigured to suppress a current flow between a source of a transistoron a substrate and the second impurity well.
 12. The semiconductordevice of claim 1, wherein the first diffusion layer and the thirddiffusion layer are separated by a first isolation region, and the thirddiffusion layer and the fourth diffusion layer are separated by a secondisolation region.
 13. The semiconductor device of claim 1, furthercomprising a guard ring provided in the substrate proximate the firstimpurity well.
 14. The semiconductor device of claim 13, wherein theguard ring comprises a third impurity well formed in the substrate. 15.The semiconductor device of claim 13, wherein the guard ring comprisesan oxide film injected into an interface formed between a side surfaceof the first impurity well and the corresponding surface of thesubstrate.
 16. The semiconductor device of claim 13, wherein the guardring comprises an oxide film injected into a trench formed in thesubstrate adjacent a side surface of the first impurity well.
 17. Asemiconductor device, comprising: a substrate; a first impurity wellformed in the substrate; a guard ring comprising an oxide film providedin the substrate proximate the first impurity well; a second impuritywell formed in the substrate; and first, second, third and fourthdiffusion layers horizontally disposed across the substrate, wherein thethird diffusion layer is disposed over the first impurity well and thefourth diffusion layer is disposed over the second impurity well. 18.The semiconductor device of claim 17, wherein the third diffusion layerand the first impurity well are configured to suppress a current flowbetween a source of a transistor on a substrate and the second impuritywell.
 19. The semiconductor device of claim 17, wherein the guard ringcomprises an oxide film injected into an interface formed between a sidesurface of the first impurity well and the corresponding surface of thesubstrate.
 20. The semiconductor device of claim 17, wherein the thirddiffusion layer and the first impurity well are configured to suppress acurrent flow between the first diffusion layer and the second impuritywell.